As is generally well recognized in the railway coupling art, light rail vehicle (LRV) couplers make use of emergency release bolts. These emergency release bolts extend radially through a draft gear tube and into a hollow shank member located behind and extending rearwardly from a coupling head. Such hollow shank member contains an energy absorbing and dissipation means. There is a coupling head disposed on a first LRV car that engages and mechanically couples to a coupling head disposed on a second LRV car. The draft gear tube disposed on each respective car is mechanically secured to the underside of its associated car.
Existing couplers normally employ a rigid hollow coupling head shank portion suspended in a draft gear tube by radially extending shear bolts. These shear bolts are designed to shear and break in two when the coupling forces between two cars which are coupled together exceeds a predetermined coupling load limit, as provided by the strength of the shear bolts.
Normally, the coupling forces that occur when a train of LRV cars is being assembled and connected together for travel with a locomotive, or lead car, exert less load on such shear bolts than the predetermined limit so that the coupling shank/draft gear tube assembly remains intact.
In contrast thereto, hard couplings or collisions between cars will exert loads in excess of the predetermined limit. When this excess load occurs the bolts shear. This allows the coupler shank portion to slide into the draft gear tube and engage and compress the energy dissipation means located in the draft gear tube. As is known in the art, such compression of the energy dissipation means helps to absorb the energy of the collision between the cars by deformation work.
In such existing couplers, the outside diameter of the coupler shank portion is less than the inside diameter of the draft gear tube in order to allow assembly of the two components and travel of such coupler shank portion into the draft gear tube during the above described collision couplings. As such, the shear bolts effect suspension of the coupler shank portion in the draft gear tube. The coupler shank portion and an integral collar do not contact the inside surface of the draft gear tube.
The shear bolts provide all the support for the coupler shank portion and are unevenly loaded when the coupler heads of two LRV cars do not contact each other squarely. An angled contact of the face portions of the coupler heads tend to place the majority of the contacting load on one side of the coupler shank portion and on those shear bolts located on that side. This occurrence can cause such shear bolts to shear prematurely and fatigue more rapidly during normal car couplings.
The above and following description is directed to light rail vehicle (LRV) type coupling, although it is believed the principles of the present invention would be useful in coupling other types of vehicles, particularly, passenger transit type railway vehicles.